U.S. Pat. No. 3,663,667 discloses a process for producing multimetal alloy powders. Thus, multimetal alloy powders are produced by a process wherein an aqueous solution of at least two thermally reducible metallic compounds and water is formed, the solution is atomized into droplets having a droplet size below about 150 microns in a chamber that contains a heated gas whereby discrete solid particles are formed and the particles are thereafter heated in a reducing atmosphere and at temperatures from those sufficient to reduce said metallic compounds at temperatures below the melting point of any of the metals in said alloy.
U.S. Pat. No. 3,909,241 relates to free flowing powders which are produced by feeding agglomerates through a high temperature plasma reactor to cause at least partial melting of the particles and collecting the particles in a cooling chamber containing a protective gaseous atmosphere where the particles are solidified. In this patent the powders are used for plasma coating and the agglomerated raw materials are produced from slurries of metal powders and binders. Both the U.S. Pat. Nos. 3,663,667 and the 3,909,241 patents are assigned to the same assignee as the present invention. Refractory metal alloys have been produced by this method, however, such materials having an average particle size of of less than about 25 micrometers.
In European Patent Application W08402864 published Aug. 2, 1984, also assigned to the assignee of this invention, there is disclosed a process for making ultra-fine powder by directing a stream of molten droplets at a repellent surface whereby the droplets are broken up and repelled and thereafter solidified as described therein. While there is a tendency for spherical particles to be formed after rebounding, it is stated that the molten portion may form elliptical shaped or elongated particles with rounded ends.
Spherical refractory metal powders such as tungsten, molybdenum, niobium, tantalum, rhenium, hafnium and their alloys are useful in applications requiring good thermal and electrical conductivity and/or endurance at high temperature and/or abrasive environments. Parts such as filters, precision press and sinter parts, injection molded parts, and electrical/electronic components may be made from these powders.
Refractory metal powders heretofore have been produced by hydrometallurgical processing. While these metal alloys are finally divided and potentially uniform in composition, they are predominantly irregular in morphology. There are applications for low surface area fine powder which requires uniform, flowable and spherical powder.
As used herein "refractory metal" means tungsten, molybdenum, niobium, tantalum, rhenium, zirconium, chromium and titanium. The term "based materials" as used herein means that the refractory metals constitute the major portion of the material thus includes the refractory metal per se as well as alloys in which the refractory metal is the major constituent, normally above about 50% by weight of the alloy but in any event the refractory metal or refractory metals are the constituent having the largest percentage by weight of the total alloy.
It is believed therefore that a relatively simple process which enables finely divided metal alloy powders to be hydrometallurgically produced from sources of the individual metals is an advancement in the art.